1. Field of the Invention
The present invention relates generally to a plunger used for forming hollow glass articles, and more particularly to a plunger which incorporates a dual cooling system therein for separately cooling different portions thereof.
1. Description of the Prior Art
Plungers used for forming hollow glass articles, such as, for example, funnels for TV glass bulbs or tubes, have a nose piece projecting outwardly of its main pressing surface which is used for forming the funnel-shaped projecting bottom part of the TV tube. Such plungers are subjected to the extremely high temperatures of the molten glass disposed within the bottom mold at the time of the press forming operation, and therefore, conventionally has cooling equipment, for cooling the same, incorporated therein.
Conventionally, such plunger cooling was performed by means of a water cooling system, however, this resulted in the refrigerant performing a uniform cooling of the entire plunger apparatus without regard to the thickness of the glass, or the shape of glass articles, in contact therewith. Consequently, due to the difference in the heat generated by means of the high temperature molten glass portions of different thickness or shape, the nose piece of the plunger, for example, wherein the wall thickness is small, became effectively excessively cooled resulting in the breakage of the glass products in contact therewith, or other defects, such as, for example, cracking of the same, or the like.
Accordingly, in order to prevent such excessive cooling, the thickness of the nose piece per se was made different, in accordance with conventional practice, however, regarding such products as the previously mentioned TV funnels, which have extreme differences in glass thickness, it is nevertheless difficult to perform adequate cooling over all parts thereof wherein the glass thickness is sometimes large and with respect to other areas wherein it is excessively thin, when using a refrigerant having an identical cooling efficiency throughout its operation. Consequently, adequate temperature control of the plunger has not been possible to obtain.